With incoming United boss Louis van Gaal keen to strengthen his defence, ex-Old Trafford defender Ferdinand said Varane would fit the bill -- but warned that it would be tough to sign him.

Nemanja Vidic has left Manchester to move to Inter Milan, while Ferdinand was released at the end of last season following a 12-year United career that saw him pick up six Premier League titles and could move to Queens Park Rangers.

United have already brought in Ander Herrera and Luke Shaw this season, and Ferdinand welcomed them both on Twitter, writing: "Congratulations to @anderherrera8 on joining a great club. It's where dreams are made into reality if you work hard."

He added: "If @ManUtd get 10 good years out of Luke Shaw then it's a no brainer. Top class young player."

The two new recruits were also welcomed in tweets from Wayne Rooney, who wrote: "@LukeShaw3 welcome to @ManUtd lad. @anderherrera8 welcome to @ManUtd mate."

Midfielder Michael Carrick tweeted: "You will love it at this great club. See you soon boys," while winger Ashley Young wrote: "Welcome... to The Biggest Club In The World! Look forward to seeing you boys soon!"